By invoking Create (Small) Magical Barrier, a magical wall (clear with a slightly blue tint) appears. The wall is rectangular, and can be up to 30ft wide and 30ft tall. The barrier is a few inches thick. The spell costs the caster 1d4 SAN loss. On invocation, the caster chooses how many MP to put into the barrier. Each 1 MP spent adds 1d10 STR to the barrier. The caster can take the barrier down in the future whenever it is their turn, without using an action.
All other creatures are stopped by the barrier. They can directly attack the barrier, attempt to pass through, or attempt to have missiles travel through the wall.
To pass through the wall, creatures make an opposed STR roll against the STR of the barrier. If they pass the STR check, they pop through the barrier to the other side.
Missiles can attempt to pass through the wall. If a player makes a ranged attack that doesn’t fail, roll attack damage (ignore all advantage/disadvantage modifiers, just roll the first die). If the attack damage is more than 1/5 the current STR of the barrier, the missile goes directly through the barrier as if it doesn’t exist, and then use modifiers to determine if you hit the target on the other side of the wall.
If a player makes a melee attack towards the wall, aims a missile at the base of the wall, or fails to have more than 1/5 the STR of the barrier on a missile attack, deal the attack’s damage against the STR of the wall. If the attack deals 1/2 the original STR of the wall or more in a single attack, the wall is instantly destroyed.